I really think they’ve shown us a good overview of what we’re about to see, including all but the final twist, which I don’t think will be Genesis. I don’t remember where I heard that it’s two chapters, but here’s my run-down:
Chapter 1: Concurrent with Chapter 8, Yuffie (in a cloak) attempts to team up with an Avalanche cell in Sector 7 that is *not* Barret’s cell after Shinra News links Avalanche and Wutai. She claims to be “an elite special forces operative of the new Wutai government.” Meaning herself. Keener-girl and Sonon agree to party up, and they need blondie to progress to Chapter 2. Shinra is chasing the guy so you go a-platformin’ to catch up with him. Keener-girl is left behind, maybe as a distraction or she gets wounded. The chase concludes with a centipede fight and Yuffie loses her cloak. Blondie gives you the keycards or whatever and it’s on to...
Chapter 2: I do believe they are either going down to Mako Reactor 0 or at least the bowels of Shinra HQ. The train scene is after Yuffie ditches the cloak so it’s likely here. We have very few clips of this chapter, but the dialogue implies that Yuffie and Sonon are separated for at least part of it, coming back together when Deepground attacks. Deepground are probably enemies in this dungeon the way those heartless guys were in 7R’s chapter 13. The final boss will be something/someone new, a gross monster or a new Tsiviet invented just for this DLC. If they tease any of DC’s Tsiviets, it will be similar to teasing Thanos at the end of the first Avengers movie. I think this will also expand on what Scarlet was doing during Chapter 16, and will likely be concurrent with that chapter. It may even show us what happens to Scarlet after the board meeting. Could she be the final boss?
I believe that Chapter 2 will also feature a combat sim for Yuffie solo and the Yuffie-Sonon team. The combat sim could be controlled by Deepground, which is why Weiss is its secret boss. It could be Weiss himself, projected by SND, or it could be some foreshadowing of digital replication, which like, sure, at this point.